During the continuous casting of molten metal in a machine using at least one moving, flexible, thin-gauge, heat-conducting casting belt, e.g., a metallic casting belt, it is vitally important that the moving belt remain travelling along a predetermined desired path requiring substantial evenness or flatness of the belt itself despite the presence of hot metal and resultant thermal stresses induced in the belt by intense heat from hot metal entering its front surface while its reverse surface is being cooled by suitable liquid coolant. The continuous casting of molten metals in a machine using at least one such casting belt often has been affected by thermally-induced warping, buckling, fluting or wrinkling (herein called "distortions") of the casting belt. Hazelett et al. in U.S. Pat. Nos. 3,937,270; 4,002,197; 4,062,235; and 4,082,101 in FIG. 8 of each Patent and Allyn et al. in FIG. 5 of U.S. Pat. No. 4,749,027 illustrate thermally-induced transverse bucking and fluting occurring in such a casting belt. Thermally-induced warping or wrinkling also has occurred in such belts. These belt distortions can occur quite suddenly, like a sudden popping of a lid on an evacuated container when the lid initially is opened and air rushes into the container. Moreover, these distortions can be erratic and unpredictable as to their extent and their particular locations in a casting belt which is intended to be even, without distortions, as it moves along the mold cavity.
Such thermally-induced distortions are more likely to occur near an input region of the mold cavity where the moving casting belt first experiences intense heating effects of hot molten metal introduced into or soon after its introduction into the moving mold cavity. Near the input region initial freezing of molten metal is occurring or commencing, and belt distortions during such freezing may result in a cast product containing slivers, stains or segregation of alloying constituents. In turn, these defects in the cast product lead to problems of strength, formability, and appearance.
C. W. Hazelett in U.S. Pat. No. 2,640,235 (in Column 7) described upper and lower cooling assemblies for upper and lower chilling bands. These cooling assemblies were identical in operation, and each cooling assembly comprised a plate that may be of some suitable readily magnetized material which formed the soft core of an electromagnet. It was the function of a plate when rendered magnetic by flow of current to pull a band toward itself. To prevent this movement of the band toward the plate, copper or brass spacers were utilized, these spacers allowing a formation of chambers between the band and the plate. In these chambers cooling water was introduced to chill the band. Even though this cooling water was introduced at considerable pressure, and sufficient normally to distort the band, the specification stated it will not do so because of the influence of the magnetic plate holding the band firmly against the rigid spacers. In this way, the specification stated, it is possible to cool the band while guiding it and holding it against distortion, and thereby maintaining accurate gauge of the product.
William Baker et al. in U.S. Pat. No. 3,933,193 disclosed apparatus for continuous casting of metal strip between moving belts. The belts were held against closely spaced support surfaces by means of externally applied attractive forces achieved by sub-atmospheric pressure conditions on the reverse side of the belts or magnetic forces employed for the same purpose.
Olivio Sivilotti et al. in U.S. Pat. No. 4,190,103 (in Column 2, lines 38-44) stated: "Thus in a practical embodiment of the above-mentioned apparatus, the belt has been drawn against the faces of the closely spaced supports by subatmospheric pressure in the water-filled housing. An alternative arrangement was to provide magnetic means, acting through ferromagnetic supports on a ferromagnetic belt, to hold the belt in the desired path."
The assignee of the present invention, Hazelett Strip-Casting Corporation, experimentally has tried stationary electromagnetic belt-backup finned platens in sliding contact with the reverse surfaces of moving casting belts but without performance which was satisfactory enough to justify their continuance in view of excessive wear and friction. Moreover, these electromagnetic finned platens failed to reliably retain or stabilize the moving casting belt in flat condition.